SINGER Joni Mitchell has revealed her private hell battling a mystery mental condition that turned her into a recluse and led her to the delusional belief she was being eaten alive by skin parasites.

Joni battled an unknown mental illness that made her think there were parasites under her skin [AFP/GETTY]

The Canadian star, who had hits with Woodstock, Big Yellow Taxi, Chelsea Morning and Both Sides Now and helped to define the counter-culture generation of the late 1960s and early 1970s, tells of her agony in a stark new biography.

Joni, now 70, also pours out her heart over “half a century of guilt” at giving up her daughter Kilauren for adoption at the age of two when she was in her early 20s.

In Joni Mitchell: In Her Own Words, conversations with Malka Marom, the eight-times Grammy winner describes how she has endured years of misery after being diagnosed with the rare condition Morgellons disease.

This causes sufferers to become convinced they are infested with insects, parasites or even contaminated hairs and fibres.

At the height of my illness I could not even wear clothing. All the time it felt like I was being eaten alive by parasites living under my skin

Joni Mitchell

Joni says in the memoir just published in America: “At the height of my illness I could not even wear clothing. All the time it felt like I was being eaten alive by parasites living under my skin. I couldn’t leave my house for several years. Sometimes it got so bad I couldn’t walk and I’d have to crawl across the floor. My legs would cramp up, just like I was having a polio spasm.”

She beat crippling polio when she was nine but all the symptoms of her childhood disease appeared to have returned as a result of the little-known and barely treatable Morgellons.

As a result she had to cancel a performance she had longed to give, at the 2010 Winter Olympics in Vancouver. Since then the condition has eased, although she has had to give up singing because “six decades of heavy smoking have finally robbed me of my voice”.

Even now she admits that she suffers from insomnia and acute paranoia and fears that whenever she leaves her Los Angeles home she is being stalked. Joni says she understands the irrationality of these feelings and accepts they are only in her mind but adds: “It all feels real. The turmoil is constant.”

The book reveals that she was barely in her 20s when she became pregnant by a boyfriend who walked out on her three months later. Before giving birth, she married former childhood sweetheart Chuck Mitchell.